One of the greatest hurdles in creating vaccines for a number of viral pathogens is the antigenic variability of viral coat proteins. The rapid mutation rate of a number of viruses (most notably influenza virus and HIV) allows the virus to escape the neutralizing antibody response induced by anti-viral vaccines. The internal proteins of the virus, on the other hand, are generally highly conserved, and have not evolved to rapidly alter their antigenicity. Antibody responses to these internal proteins, while a consistent feature of immune responses to viruses, almost always fail to influence viral infectivity, since the antibodies do not have access to their target antigens, which are located either inside the virus, or inside the virus infected cells. If however, antibodies are introduced into the cytosol of cells, they do have the ability to prevent viral infection. Recent advances in understanding antibody folding indicate that antibodies have the ability to properly fold and bind antigen when they are expressed in the cytosol by removing their amino terminal ER insertion sequences. Therefore, cells, or eventually, transgenic animals expressing such cytosolic antibodies should be resistant to virus infection. Using electroporation to introduce antibodies into the cytosol, we identified antibodies able to block infection of cells with influenza viruses. In the past year we have cloned the heavy and light chain genes from a hybridoma secreting an antibody that is able to block infection with any of the human influenza A virus subtypes. After removing the portion of the genes encoding the ER insertion sequence, we have inserted these gene into eukaryotic expression vectors, and have transfected cells with the vectors. We are in the process of characterizing the expression and folding of these cytosolic antibodies, and the resistance of antibody expressing cells to influenza A virus infection. Our goal is to create transgenic animals resistant to influenza virus infection.